JPS6216365A - Plastic vessel displaying release seal and manufacture thereof - Google Patents

Abstract

A polyolefin container (11) is disclosed which is hermetically sealed with a complementary lid (13) extending across the open container the opposed faces of the container surface and the lid being bonded together by a peelable, heat seal layer (19) intermediate between the opposed faces. The heat seal layer is comprised of a mixture of a particulate filler and first and second polyolefin resins, the second polyolefin resin having a melt flow rate at least about three times greater than the melt flow rate of the first polyolefin resin.

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to thermoprocessable plastic containers for foodstuffs susceptible to oxidative deterioration, and more particularly to such containers having peelable, distress-resistant lids.

In recent years, the food packaging industry has grown increasingly interested in plastic packaging, which eliminates the need for expensive, energy-intensive refrigerated transportation and storage equipment, due to the fact that, among other advantages, it does not require refrigeration for preservation. Shows a strong interest in the concept of food. In addition to withstanding the rigors of sterilization and subsequent reheating and providing sufficient gas and moisture barrier properties to adequately protect the contents during storage, they can be easily removed from the container without splitting or breaking the packaging material. Significant efforts have been made to develop rigid or semi-rigid retortable or autoclavable plastic food containers that can be effectively hermetically sealed with peelable lids. In conjunction with the peelable opening feature, it is desirable for the food container to be operable by manually pulling the lid off the container instead of relying on a knife, scissors, or opening knob to open the package.

Among the materials considered for use in making the food containers are laminated films of polyolefins such as polyethylene, polypropylene, and copolymers thereof, such as ethylene-propylene copolymers. The gas permeability of laminated polyolefin films is reduced by incorporating into the laminated film structure an inner layer of a gas barrier film, such as a nylidene chloride polymer (eg, Saran) or a deicing ethylene/vinyl acetate copolymer.

Containers are manufactured from these laminated films. For example, the desired shape is given to the laminated film by thermoforming. The container body generally has a bottom and sidewalls extending upwardly from this bottom, and thus can be a type of dish or pail of cylindrical, truncated, square, rectangular, or polygonal shape, depending on the characteristics of the product to be packaged. to accomplish.

The container is hermetically sealed with a protective cover or lid.

To this end, the side wall of the container terminates at its upper end with a flat collar pointing radially outward, and the lid rests flat on the polyolefin collar surface and is placed under high pressure (e.g. 601) Si).
It is sealed under high temperature (eg 300°C).

Heretofore, lidding materials have been used that are at least 0.10 mil thick aluminum foil or a laminate of, for example, aluminum foil and one or more thermoplastic films such as polyethylene or polypropylene. The surface of the aluminum column foil that is heat-sealed to the polyolefin collar is provided with a heat-activated bond-promoting layer that enables the foil to be heat-sealed to the collar. Adhesive coating compositions that have been investigated for bonding aluminum foil layers to polyolefin collars include epoxy resins, ethylene-vinyl acetate copolymers, and carboxyl-modified polypropylenes such as ethylene-vinyl acetate copolymers.
Maleic anhydride adducts of propylene copolymers, one of which, Wang-Prime (Morton Chemicuff, Inc., Morton Noritsuji Products), is approved by the Federal Drug Administration for use in food packaging], etc. and is commercially available.

Heat sealing the adhesive coated aluminum foil lid to the polyolefin container brim is generally sufficient to ensure that the package remains hermetically sealed during normal handling and during shipping and storage.

Although heat sealing of an aluminum foil lid to a polyolefin-container brim via a heat-activated bond-promoting layer is highly effective in bonding the lid to the brim, the strength of the heat seal is limited by its use for manufacturing the lid. Attempts to remove the heat-sealed lid would result in part of the lid sticking to the tsuba surface, resulting in an unesthetically rough surface of the tsuba in the heat-sealed area, which is unacceptable from a consumer appeal standpoint. It has also been experimentally determined that it has a jagged appearance. Furthermore, due to the high strength bond, the force required to remove grass is too high to be widely accepted by consumers.

Attempts to weaken the heat seal in order to obtain a hermetically sealed container that can be easily opened or peeled from the container brim will result in a seal of insufficient mechanical strength; Packages may be opened accidentally when dropped from containers or otherwise abused during normal handling and shipping.

Accordingly, it is an object of the present invention to provide a peelable, hermetically sealed thermoprocessable polyolefin plastic food container.

It is generally an object of the present invention to provide a seal that can be peelably sealed and that can resist accidental opening when dropped from a height or subjected to mechanical abuse during handling and transportation. An object of the present invention is to provide a sealed polyolefin food container.

According to the present invention, there is provided a method for manufacturing a polyolefin container that can be hermetically sealed with a peel-openable lid, the method including a particulate filler between the lid to be sealed and the surface of the container. and a first and second polyolefin resin, wherein the second polyolefin resin has a melt flow rate at least about three times greater than the melt flow rate of the first polyolefin resin; The combination of special granular filler, which is characterized by applying pressure to form a hermetic seal, and multiple polyolefin resin materials with different melt flow rates results in heat sealing, where the cohesive strength of the intermediate layer is smaller than the bonding strength of heat sealing. Since it forms an intermediate layer,
Cohesive failure of the intermediate layer when attempting to separate the lid from the container allows for easy peeling of the lid from the already heat-sealed container surface.

In a mechanical abuse test, containers hermetically heat sealed and then retorted according to the method of the present invention
found to resist accidental enclosure under conditions that meet the LJSDA Mechanical Abuse Specification for Food Containers.

According to the present invention, the container may be manufactured from one or more polyolefin materials or by one of the conventional coextrusion methods.
The polyolefin may be manufactured from multilayer sheet structures made by lamination of individual layers utilizing two or by lamination of separately formed sheets of individual polyolefin layers together.

In such laminated structures, the polyolefin outer layer may have a thickness of about 10 to about 60 mils, preferably about 15 to about 30 mils. As used herein, the term "polyolefin" refers to polyethylene, polypropylene, and random copolymers of ethylene and/or propylene or other copolymers containing less than 50% by weight of other olefinically unsaturated monomers. means a block copolymer of ethylene and propylene.

To produce food containers with reduced air permeability,
A layer of extrudable gas barrier synthetic resin is used as the barrier inner layer for H4
1 structure.

A wide variety of extrudable barrier resins can be used as barrier inner layers according to the present invention. Extrudable vinylidene chloride polymers and ethylene vinyl alcohol copolymers are particularly suitable as gas barrier layers. The requirements for the barrier inner layer are that the material be laminated to another polymer layer and that the laminate have the desired gas barrier properties. Extrudable compositions of nylidene chloride polymers containing at least 70% by weight of vinylidene chloride, with the remainder copolymerizable with one or more olefinically unsaturated monobases, e.g. vinyl chloride, are particularly preferred. Beneficial and advantageous. Ethylene vinyl alcohol copolymers are derived from ice-melting ethylene vinyl acetate copolymers containing 15-65 mole percent ethylene and 85-35 mole percent vinyl acetate.

The gas barrier inner layer of the laminate structure may be about 0.2 to about 3.5 mils thick, most preferably about 1.0 to about 2.5 mils thick. The gas barrier inner layer has a thickness of about 0.2 to about 0
．． It is adhered to the polyolefin outer layer by an adhesive layer which can vary between 4 mils, but the generally preferred adhesive layer thickness is from about 0.25 to about 0.35 mils. Ethylene vinyl acetate copolymer is commonly used as the adhesive layer.

In making the peelable heat-sealable interlayer used in the practice of the present invention, the first polyolefin resin used to make the heat-sealable interlayer composition comprises about 45 to about 60% by weight of the interlayer composition. % of the composition, preferably about 40% of the composition.
~ Approximately 55 times 4%.

The first polyolefin resin is about 3 to about 8 at 230°C.
do/win, preferably about 4 at 230°C
~(Has a melt flow rate in the range of 3 dg/sin.

The second polyolefin resin used to make the heat seal interlayer of the present invention is about 10 to 10% of the middle layer composition.
It comprises about 40%, preferably about 15% to about 30% of the composition. The second polyolefin resin has a melt flow rate ranging from about 15 to about 50 dMln at 230°C, preferably from about 20 to about 306 o/gain at 230°C.

The term "melt flow rate" is a term in the polymer art and is a measure of the rheological properties of a polymer.

Melt flow rate characterizes the processability of a polymer and is also an approximate indicator of polymer molecular weight. That is, as the melt flow rate increases, the molecular weight decreases.

The melt flow rate of polyolefins such as polypropylene is typically measured according to ASTM Test D-1238 (Condition L). In this test, (0.082 diameter
5 and 0.315 inch long orifice)
The extrusion rate, expressed in grams per 10 minutes, is 23
Measurements are made on the polymer at 0° C. on a "dead weight bis-I blastometer" under the load of a piston having a diameter of 0.373 inches and having a weight of 21609 with the plunger.

In the manufacture of polyolefin food containers according to the present invention in which the brim surface of the container is to be heat-sealed to the lid via the peelable P1-seal interlayer, the resin composition of the heat-seal interlayer preferably has a 6do/
Generally less than sin, about 5.0 dd/at 230°C
A first polyolefin resin having a melt flow rate of Win = 1 and a third polyolefin resin preferably less than about 40 at 230°C.
and a second polyolefin resin having a melt flow rate of 0 do/win.

It is essential to the practice of this invention that the interlayer consists of a blend of polyolefin resins having widely different melt flow rates. If polyolefin resins with different melt flow rates are not used at the specified m degrees, the desired combination of strippability and mechanical abuse resistance properties is no longer obtained. As explained later,
polyolefin resin with a higher melt flow rate,
Of the middle class at a concentration exceeding the above specified! 1! When used in J construction, the layer is too brittle to be suitable for practical use. If less than 40% of the lower melt flow rate resin is used in the preparation of the heat seal layer composition, the peel seal will meet the USDA
Fails to pass mechanical abuse tests or only marginally passes such tests.

The filler contained in the heat seal interlayer generally comprises about 25% to about 40%, preferably about 30% to about 35% by weight of the layer composition. The filler preferably has a flake-like structure and is preferably used in finely divided form, between 0.1 and 10.0
Particle sizes on the order of microns are preferred. Suitable filler materials include silica, talc, mica, etc., with talc being preferred.

Various pigments and colorants may be added to the polyolefin composition to impart color or opacity. Pigments and colorants range from about 1% to about 10% by weight of the heat seal layer composition. 1 may be contained in the polyolefin composition.

In the manufacture of the containers of the invention, the heat-sealing intermediate layer may be applied in the form of a thin strip to the lid or container brim, or either to the lid back side or to the container brim surface containing the heat-activated layer. It may also be a dispersion that can be prepared.

Preferably, the heat seal intermediate layer has a thickness of about 2 ms to the polyolefin outer layer of the laminated sheet material forming the container.
Coextruded as ~10 mil layers.

Any suitable sealing format can be used to heat seal the lid to the container, including ultrasonic sealing, induction heating, or heat sealing jaws.

As shown in FIGS. 1 and 2, the present invention very generally has a central recess 12 and an outwardly curved horizontal 112a to which the lid 13 is heat sealed. The package 10 has a unique WAm container or cup 11.

FIG. 3 shows a partial cross-section of the package 10, the container 11 being molded from a multilayer film structure.

Lid 13 hermetically seals volume 1811. Part of the lid is Tsuba 1
2a to form a grip area 13a, the grip can be grasped with fingers and peeled off from the collar to enclose the package.

The laminated structure of the container 11 includes a gas barrier core inner layer 14 and a thermoplastic adhesive wJ1 juxtaposed on both sides of the barrier 11114.
5.16, polyolefin outer JIi 17 and 18 adhered to each of its adhesive layers 15 and 16, and
Consisting of a continuous cohesive heat seal 11119 made of the high melt flow rate and low melt flow rate polyolefin resin of the present invention and a granular filler,
The heat seal layer is bonded to the polyolefin outer layer 18 to form the interior food contact surface of the container 11.

The total thickness of the multilayer structure forming the container 11 is about 10 to
The thickness ranges from about 100 mils, preferably from about 10 to about 40 mils. The heat seal layer 19 has a thickness of about 1 to about 10
Mil thickness, polyolefin outer ff117.18
has a thickness of about 10 to about 60 mils, gas barrier layer 14 has a thickness of about 0.2 to about 0.35 mils, and adhesive weight 5° 16 has a thickness of about 0.25 mils. It can have a thickness.

Lid 13 constructed of an aluminum foil layer 21, inner and outer heat-activated thermoplastic adhesives WI 22 and 23 juxtaposed on either side of the aluminum foil layer 21, and a polyolefin layer 24 bonded to the outer adhesive layer 23. is heat sealed to container 11 via an intermediate peelable heat seal layer. The overall thickness of the lid ranges from about 15 to about 40 mils thick, preferably from about 10 to about 30 mils thick.

The aluminum foil WI21 has a thickness of about 1-5 mils;
The inner and outer adhesives WJ22 and 23 are approximately 0.1
~ about 2.5 mils thick, and the remaining polyolefin layer has a thickness of about 25-30 mils h J
I can do two things.

In order to hermetically seal the container 11, 1113 is attached to the container 11.
are placed over the bare heat seal layer 19 of the flanges 12a, h, and heat and pressure are applied by the platen of a heat seal device, such as an induction heater, to form a hermetic seal. During the heat-sealing operation, the polyolefin material of heat-sealing layer 19 is bonded to heat-activated surface layer 22 of lid 13.

The sealed container is sufficiently rigid to retain its shape during normal handling.

In the practice of the present invention, optimal results are obtained when the heat source used for the heat seal operation is applied to the package component opposite the surface on which the heat seal layer is provided.

The heat sealing operation results in a hermetically sealed container, but
Even after the lid 13 has been exposed to heat processing, it can be easily and smoothly pulled off by hand without tearing either the lid 13 or the collar 12a by grasping the N13 with the knob 13a and peeling it from the collar. be able to. The heat seal layer 19 in the heat seal area is reduced in thickness when the N13 is peeled off from the collar 12a because a portion of the heat seal layer 19 is separated and removed from the collar surface from which the lid 13 is peeled off. heat seal 11119
The cohesive strength of heat seals! This ease of separation is achieved because the tensile strength of the bond between the surface of 1119 and the surface of the thermally active layer 22 of the lid 13 is significantly less than the tensile strength of the bond. The inspection of the back surface of the lid that has been pulled apart is the heat-activated bottom surface II of the lid 13! A continuous bead of heat seal material 19 is shown attached to 122 .

In this way, a polyolefin container is obtained which is hermetically sealed but can be easily peeled for manual opening by the user without resorting to scissors or other tools. This sealed container can be retorted without premature sealing despite being peelably openable, and will not accidentally seal when dropped from a height of two feet or more. , and will not be opened accidentally when subjected to the normal mechanical abuse encountered during transportation and storage.

The present invention is illustrated by the following examples. A 18% layered sheet of Yutaka Futtomo consists of 55% by weight of polypropylene having a melt flow rate of 5, 15% by weight of polypropylene having a melt flow rate of 1 to 30, and 2 microns of polypropylene. It was produced by coextrusion of first and second sealable layers consisting of a mixture of 25% by weight talc with a particle size of 1 micron and 5% titanium dioxide with a particle size of 1 micron. The heat seal layer was bonded to one of the two outer layers of polypropylene in the sheet. Vinylidene chloride 8
An inner barrier layer consisting of 2% by weight vinyl acetate and 18% by weight vinyl chloride was interposed between the outer polypropylene layer and bonded thereto by an adhesive layer consisting of an ethylene-vinyl acetate copolymer containing 28% by weight vinyl acetate. The outer polypropylene layer on one side of the laminate sheet is pigmented with 8% by weight brown pigment, and the outer polypropylene layer on the other side, which constitutes the internal food contact surface, is colored with 1% titanium dioxide 6ffi.
It was colored with. The heat seal layer was bonded to the titanium dioxide colored polypropylene layer. The heat seal layer was 5 mils thick. The outer layer has a thickness of 20 mils;
The gas barrier inner layer had a thickness of 2.2 mils and the adhesive layers each had a thickness of 0.25 mils. The individual layers were coextruded from a conventional extruder through a flat sheet die. The melt streams were combined in a coextrusion block before being extruded from the die.

The multilayer coextrusion is made into 6.55" by conventional thermoforming equipment.
A dish measuring 5.0" x 1.0" was thermoformed with the heat seal layer forming the food contacting surface of the dish.

Complementary lids were manufactured as follows: First, both sides of a 1.5 mil thick film of aluminum foil were coated with 0.2 ml of Morprime, a commercially available maleic anhydride-based polypropylene-containing adhesion-promoting dispersion. Coated with a mil thick coating. Upon application of Morprime, the coated aluminum foil was baked at 180° C. to evaporate the solvent and coalesce to coalesce the dispersed particles into a continuous film. A 23 mil thick film of titanium dioxide colored polypropylene was then extrusion coated onto one side of the Morprime coated aluminum foil.

This lid was used to hermetically seal a water-filled thermoformed dish by heat sealing the Morprime coated surface of the lid to the brim surface of the dish. Place the lid/container assembly between the jaws of the induction sealer and apply the W/10 to the Totsuko 50.
Heat sealed using a KIIZ induction heater at 300° C. and 60 psi for 0.3 seconds.

A 1.0 inch piece was cut from the lid and induction heat sealed to an equally sized piece cut from the laminated sheet from which the container was thermoformed. T-peel values, ie, the force required to separate the heat-sealed layers, were measured on an Instron tensile testing machine applying a constant strain rate of 2.0 inches per minute on the assembly. T-peel values are recorded in the table below.

The procedure of the above example was repeated except that the talc matrix in the heat seal layer was increased to 30% by weight and the melt flow rate 5 polypropylene was reduced to 50% by weight. The T-peel values for this heat seal layer are also recorded in the table below.

This heat-sealed water-packed blood is heated at 250° for 0.5
Retorted for an hour. It took 0.5 hour for the retort to reach a temperature below 250°C.

When attempting to pull the heat-sealed lid off the retorted container collar, the lid could be easily peeled off the container by hand. Inspection of the lid and tsuba surfaces that were heat-sealed together and retorted shows that some of the heat-seal layer was removed with the lid and some of the heat-seal layer remained on the tsuba surface; This indicates that there was cohesive failure.

The ability of retorted heat-sealed containers to withstand mechanical abuse was determined according to the US Department of Agriculture's Standardized Mechanical Abuse Test as follows.

1. Vibration Test Sealed containers were subjected to vibration in a test device designed to briefly simulate the vibrations that packages would encounter during normal shipping operations. In this test, the package was placed on a vibrator for 30 minutes at approximately 200 cycles/minute.

2. Drop test (ASTM D775-61) ASTM
After vibration testing with D999-TS, a sealed container filled with 10 ounces of water withstood a drop onto a hard surface from a height of at least 28 inches made so that the corners called 2-3-5 were impacted. 3.
The -5 edge was dropped again so as to receive an impact, and the 5-edge, No. 2-id, and 3-bottom were each dropped three more times in order so that they all received an impact.

No leaks were detected even after dropping the vibrated container from a height of 42 inches.

The procedure of the above example was repeated except that the concentrations of high melt flow rate and low melt flow rate resins were varied as well as the concentration of talc filler. The T-peel values and the ability of the heat-sealed containers to withstand a drop of at least 28 inches after being subjected to vibration testing and being tolerated are recorded in the table below.

For comparison purposes, the procedure of the example was repeated except that talc concentrations and high and low melt flow rate polypropylene resin concentrations and proportions outside the range of the present invention were used to prepare the heat seal layer. . The results of these comparative tests, designated rCJ, are also recorded in the table below.

If an attempt was made to produce the heat sealing composition below according to the procedure of the example, the resulting composition would form a brittle layer that would easily fracture when heat sealed, thus causing the material to fail with obvious failure. Since it was clear that

Heat seal layer weight ω% Weight% Weight% Polypropylene Talc Titanium dioxide melt flow rate 30 0.6

[Brief explanation of the drawing]

FIG. 1 is a plan view of a package of the type that is advantageously sealed in accordance with the present invention. FIG. 2 is a side view of the package shown in FIG. 1;
and FIG. 173 is a partial cross-sectional view with exaggerated detail showing each layer of the laminated container structure and the surfaces sealed in accordance with the present invention.

Claims (1)

[Scope of Claims] (1) A package consisting of a polyolefin container having a complementary lid extending across an opening of the container, wherein the contacting faces of the container and the lid are formed by a peelable heat-sealing layer between the facing faces. joined together by an inclusion, the heat seal layer comprises a mixture of a particulate filler and a first and second polyolefin resin, the second polyolefin resin having a melt flow rate at least about three times greater than the melt flow rate of the first polyolefin resin. A package having a flow rate. (2) the heat seal layer comprises about 40 to about 80% by weight of a first polyolefin resin having a melt flow rate of about 2 to about 8; and about 10 to about 80% by weight of a second polyolefin resin having a melt flow rate of about 20 to about 60; 25% by weight and about 15 to about 50% by weight particulate filler. (3) The granular filler is talc, Claim 2
package of terms. (4) The package of claim 1, wherein the first and second polyolefin resins are polypropylene. (5) The first and second polyolefin resins are ethylene-
The package of claim 1 which is a propylene copolymer. (6) The package according to claim 1, wherein the melt flow rate of the second polyolefin resin is six times the melt flow rate of the first polyolefin resin. (7) The package according to claim 1, wherein the polyolefin container is formed from a laminated film structure whose outer layer is formed from polypropylene. 8. The package of claim 7, wherein the laminated film structure is provided with an inner gas barrier layer sandwiched between outer polypropylene layers. 9. The package of claim 8, wherein the gas barrier inner layer is formed from a vinylidene chloride polymer. (10) The package of claim 1, wherein the lid consists of a bonding layer of aluminum foil and a heat-activated carboxyl-modified polypropylene layer from the outside inward. 11. The package of claim 1, wherein the heat seal layer is an integral part of the container. (12) A method for manufacturing a peelably heat-sealed container lid and a container component formed from a polyolefin resin, wherein the lid and the container component have facing surfaces that are hermetically heat-sealed to each other; At least one of the opposing faces is provided with a heat-sealable layer whose cohesive strength is less than the tensile strength of the layer so that when a force is applied to the part to separate them, the layer cleaves within itself. wherein the heat seal layer comprises a mixture of a particulate filler and a first and second polyolefin resin, the second polyolefin resin having a melt flow rate at least about three times greater than the melt flow rate of the first polyolefin resin; A method characterized by: (13) The heat seal layer comprises about 40 to about 80% by weight of a first polyolefin resin having a melt flow rate of about 2 to about 8 and about 10 to about 80% by weight of a second polyolefin resin having a melt flow rate of about 20 to about 60. 13. The method of claim 12, comprising a mixture of 25% by weight and about 15 to about 50% by weight particulate filler. (14) The method according to claim 12, wherein the particulate filler is talc. (15) The method of claim 12, wherein the first and second polyolefin resins are polypropylene. (16) The method of claim 12, wherein the first and second polyolefin resins are ethylene-propylene copolymers. (11) The method according to claim 12, wherein the melt flow rate of the second polyolefin resin is six times the melt flow rate of the first polyolefin resin. (18) The method of claim 12, wherein the polyolefin container is formed from a laminated film structure whose outer layer is formed from polypropylene. (19) The laminated film structure has an inner gas barrier layer sandwiched between outer polypropylene layers.
Section method. (20) The method of claim 19, wherein the gas barrier inner layer is formed from a vinylidene chloride polymer. 21. The method of claim 12, wherein the lid consists of a bonding layer of aluminum foil and a heat-activated carboxyl-modified polypropylene layer from the outside inward. 22. The method of claim 12, wherein the heat seal layer is an integral part of the container. (23) The method of claim 12, wherein the heat sealing heat source is applied to a surface opposite the surface on which the heat sealing layer is provided.